本文是对文章Intel and AT&T Syntax的中英文对照翻译。
Intel and AT&T syntax Assembly language are very different from each other in appearance, and this will lead to confusion when one first comes across AT&T syntax after having learnt Intel syntax first, or vice versa. So lets start with the basics.
Intel汇编语言和AT&T汇编语言在语法外观上差异很大，这会让那些首先学过Intel汇编语法的人在
首次接触AT&T语法的时候感到困惑，反之亦然。 因此，我们接下来对基本的语法做一个对比。
1. Prefixs. 前缀
In Intel syntax there are no register prefixes or immed prefixes. In AT&T
however registers are prefixed with a ‘%‘ and immed‘s are prefixed with a ‘$‘.
Intel syntax hexadecimal or binary immed data are suffixed with ‘h‘ and ‘b‘
respectively. Also if the first hexadecimal digit is a letter then the value
is prefixed by a ‘0‘.
在Intel语法中，不存在寄存器前缀或立即数前缀。但是在AT&T语法中，寄存器以‘%‘为前缀，立即数则
以‘$‘为前缀。 在Intel语法中，十六进制立即数以‘h‘结尾，二进制立即数则以‘b‘结尾。另外，如果
十六进制立即数的首个数字是字符(a-f),则需要在此十六进制立即数的前缀上冠以‘0‘。
Example:
| Intel Syntax | AT&T Syntax |
| mov eax, 1 | movl $1, %eax |
| mov ebx, 0ffh | movl $0xff, %ebx |
| int 80h | int $0x80 |
2. Direction of Operands. 运算方向
The direction of the operands in Intel syntax is opposite from that of AT&T syntax. In Intel syntax the first operand is the destination, and the second operand is the source whereas in AT&T syntax the first operand is the source and the second operand is the destination. The advantage of AT&T syntax in this situation is obvious. We read from left to right, we write from left to right, so this way is only natural.
在运算方向上，Intel语法与AT&T语法证号相反。 在Intel语法中，第一个操作数是目标，第二个
操作数为源，然而在AT&T语法中，第一个操作数为源，第二个操作数为目标。在这种情形下，AT&T
的语法优势是显而易见的，(因为)我们读的时候从左至右读，写的时候从左至右写。因此，这种方法
才是自然而然的，符合人的读写习惯。
Example:
| Intel Syntax | AT&T Syntax |
| instr dest, source | instr source, dest |
| mov eax, [ecx] | movl (%ecx), %eax |
3. Memory Operands. 内存运算
Memory operands as seen above are different also. In Intel syntax the base register is enclosed in ‘[‘ and ‘]‘ whereas in AT&T syntax it is enclosed in ‘(‘ and ‘)‘.
从上面的例子可以看出，Intel语法和AT&T语法在内存运算也是不同的。 在Intel语法中，基址寄存器
是被‘[‘和‘]‘ (方括号)括起来的，而在AT&T语法中，它是被‘(‘和‘)‘(园括号)括起来的。
Example:
| Intel Syntax | AT&T Syntax |
| mov eax, [ebx] | movl (%ebx), %eax |
| mov eax, [ebx+3] | movl 3(%ebx), %eax |
The AT&T form for instructions involving complex operations is very obscure compared to Intel syntax. The Intel syntax form of these is segreg:[base+index*scale+disp]. The AT&T syntax form is %segreg:disp(base,index,scale).
与Intel语法相比，涉及复杂操作指令的AT&T语法格式是非常晦涩的。
Intel语法格式是 segreg:[base + index * scale + disp]，
AT&T语法格式则是%segreg:disp(base, index, scale)。 Index/scale/disp/segreg are all optional and can simply be left out. Scale, if not specified and index is specified, defaults to 1. Segreg depends on the instruction and whether the app is being run in real mode or pmode. In real mode it depends on the instruction whereas in pmode its unnecessary. Immediate data used should not ‘$‘ prefixed in AT&T when used for scale/disp.
index/scale/disp/segreg都是可选的，可以简单地给省略掉。scale， 如果未指定并且指定了索引，
则默认为1. segreg取决于指令以及应用程序是否以实模式或保护模式运行。在实模式下，它取决于指令，
而在保护模式下它不必要。使用立即数时，在用于scale/disp的时候，不应在AT＆T语法中使用‘$‘前缀。
Example:
| Intel Syntax | AT&T Syntax |
| instr foo, segreg:[base + index * scale + disp] | instr %segreg:disp(base, index, scale), foo |
| mov eax, [ebx + 20h] | movl 0x20(%ebx), %eax |
| add eax, [ebx + ecx * 2h] | addl (%ebx, %ecx, 0x2), %eax |
| lea eax, [ebx + ecx] | leal (%ebx, %ecx), %eax |
| sub eax, [ebx + ecx * 4h - 20h] | subl -0x20(%ebx, %ecx, 0x4), %eax |
As you can see, AT&T is very obscure. [base + index * scale + disp] makes more sense at a glance than disp(base, index, scale).
4. Suffixes. 后缀
As you may have noticed, the AT&T syntax mnemonics have a suffix. The significance of this suffix is that of operand size. ‘l‘ is for long, ‘w‘ is for word, and ‘b‘ is for byte. Intel syntax has similar directives for use with memory operands, i.e. byte ptr, word ptr, dword ptr. "dword" of course corresponding to "long". This is similar to type casting in C but it doesnt seem to be necessary since the size of registers used is the assumed datatype.
Example:
| Intel Syntax | AT&T Syntax |
| mov al, bl | movb %bl, %al |
| mov ax, bx | movw %bx, %ax |
| mov eax, ebx | movl %ebx, %eax |
| mov eax, dword ptr [ebx] | movl (%ebx), %eax |
注： nasm采用的是Intel的语法。关于[base + index * scale + disp], 下面给出一个截图以详细说明。
原文：http://www.cnblogs.com/idorax/p/6430884.html